Salmonella: An opportunistic killer

The calls all have a similar ring to them. "I perform DA surgeries on many farms, but, on this one farm, the animals tend to die. Why is that?"

John House, associate clinical professor of veterinary medicine at the Veterinary Teaching Hospital at the University of California-Davis, often fields calls from veterinarians when things don't go as expected. In the above scenario, and in many others like it, the culprit lurking in the background tends to be salmonella.

"It's an opportunistic pathogen," explains House. "When things get out of synch, such as when an animal is compromised, salmonella can strike." Once an outbreak starts, sick animals shed the organism, which multiplies the contamination in the environment and puts healthy animals at risk.

Salmonella commonly strikes in the hospital pen, fresh-cow pens and in calves. Producers often treat sick animals with antibiotics, but with salmonella, the animals don't necessarily get any better, says Craig Meadows, veterinarian in Turlock, Calif.

In animals showing clinical signs of salmonella, death losses can be as high as 20 percent to 50 percent, says Meadows. But, it doesn't have to be that way. Once producers learn what they are dealing with, they can limit the spread when an outbreak occurs, and even minimize the chance of another oubreak occurring.

Use these five steps to do just that.

1. Know the signs

In order to get a quick jump on salmonella, and limit its spread, you have to know the clinical signs, says George Barrington, assistant professor in large animal medicine at Washington State University. Depending on the age of the animal, its level of immunity and virulence of the salmonella strain, it will manifest itself in one of three ways: peracute septicemia, acute enteritis or chronic enteritis. The most common signs include diarrhea - often with blood or mucus in it, fever, depression, down animals, off feed, dehydration and bloodshot eyes.

Once you identify an animal with clinical signs, test to confirm which strain is present. Although 2,200 serotypes of salmonella exist, only about 10 commonly affect cattle, explains Barrington.

Fecal, blood and, tissue samples from dead animals can all be used to identify the strain. In farms where salmonella has struck before, oftentimes it is the same strain coming back to haunt you. However, most farms have several strains of salmonella lurking in the background. So, before you give any antibiotics, determine which serotype is present and what antibiotics it is sensitive to, stresses House.

2. Isolate animals with clinical signs

Immediately isolate all animals with clinical signs, says Meadows. If, for example, you have one cow with clinical signs in a fresh-cow group of 25, you need to remove and isolate that one animal. Consider all of the remaining animals in that group as "at risk" and quarantine them.

Research has shown that some cows shed salmonella without ever developing clinical signs. So quarantining the rest of the group is an important step. While quarantined, no new animals should enter the group, or leave the group. Watch for clinical signs, and if possible, take daily rectal temperatures, suggests Meadows. A sudden fever is one of the first warning signs that an animal is infected with salmonella.

Infected animals shed salmonella in their feces, urine, nasal secretions and saliva. The incubation period ranges from one to four days. So, if none of the other animals in that group develop clinical signs after four days, you can remove the quarantine.

With calves showing clinical signs, be sure to confine to an individual pen and do not allow to suckle other calves.

Isolation can be impractical in some herds. In those cases, treat the entire group as infected and take measures to prevent the spread of salmonella to other groups.

3. Prevent transmission

Once you have animals isolated, make sure your employees don't unknowingly transfer the pathogen to another group of animals, says Barrington. Use these guidelines:

Care for and feed infected animals last. When done, employees should change coveralls, wash their hands with soap and water and scrub and disinfect boots.

If you use a skid-steer to clean out pens in an infected area, clean and sanitize it before using in an uninfected animal area.

Do not use the same tractor and loader to clean pens and handle feed. If you have to, disinfect equipment before using it to load feed.

Do not allow sick animals to wander loose around the dairy.

4. Limit animal stress
This is the area that makes or breaks producers' success with salmonella.

When salmonella breaks on most farms, it is not the first time the animals have been exposed to it, says House. Salmonella is commonly found in the environment. But it can only strike when an animal's immunity is compromised, or when environmental conditions have deteriorated - for example, muddy lots, dirty maternity pens - and allowed salmonella to multiply. In fact, research has shown that a healthy cow can withstand a challenge dose of salmonella at 10 to the 11th power. A cow that is stressed or off feed, however, may succumb to a challenge dose of just 100 salmonella, says House.

Outbreaks of salmonella reflect insecure management practices. In short, your security system to protect animal health has failed. To limit the spread, and prevent it from reoccurring, you must find the weak link that allowed salmonella to break.

Start your search where the outbreak occurred. Use the following list of questions - grouped according to the most common areas where salmonella occurs - to help identify the stressor(s) that allowed salmonella to gain a foothold. Then, take action to immediately correct the problem.

Fresh cows/hospital cows

Nutrition - When cows are eating, the volatile fatty acids (VFAs) produced in the rumen prevent salmonella from flourishing. However, when she goes off feed, VFA levels drop. Ask yourself these questions to see if nutrition might be the root of the problem:

Is she eating at all?

Has dry matter intake suddenly dropped?

Is the ration correct?

Is the feed spoiled? Moldy? Contaminated with manure?

Does she have access to feed whenever she wants it?

If using anionic salts, have you checked urine pH to make sure the anionic salts are not depressing feed intake?

Can manure, or flush water, from the hospital pen run downhill to the fresh-cow pen?

Calves
Calves generally get exposed to salmonella in the maternity pen. Dirty pens, nursing on manure-coated teats, and receiving colostrum from a salmonella-infected cow can all infect a calf. Whether or not she develops clinical signs depends on how well you limit stress. Use this checklist to help determine if you can improve in this area.

Is the maternity pen clean and dry?

Did she receive enough quality colostrum?

Was it received within the first 12 hours of life?

Are you feeding enough calories to meet the calf's needs? (Remember in the winter, and during cold, wet periods young calves need extra calories to fight off a disease challenge.)

Is her calf pen clean and dry?

Is she given fresh water and calf starter daily?

Are hutches cleaned and sanitized between each calf?

When feeding milk from the hospital pen, how much time elapses between harvest and feeding?

If you store waste milk, is it refrigerated to prevent bacterial growth? (If stored in a 5-gallon bucket, no refrigerator can cool it fast enough to prevent bacterial growth.)

Is milk from the hospital pen pasteurized before being fed to calves?

Does manure from the hospital pen flow downhill to calf pens?

Is flush water from the cow barns also used to flush calf alleys?

5. Use supportive therapy

If you've got salmonella, you need to bring your veterinarian in to help. Several strains of salmonella are resistant to antibiotics and your veterinarian will be able to tell you which strain you have and what treatments might be helpful.

However, several supportive therapies can be used to help limit death loss. Start by keeping the animals hydrated. In cows, options include delivering a liter of hypertonic saline solution intravenously twice a day, and/or drenching with electrolytes and water. A mixture of 5 to 10 gallons of water mixed with 150 grams of lite salt (potassium chloride) and 25 grams of calcium chloride works well

To keep calves hydrated, use an esophageal feeder to deliver electrolytes, and IV fluids if deemed necessary by your veterinarian.

For cows with diarrhea, pharmaceutical-grade liquid charcoal can be helpful. In calves, where Salmonella dublin and Salmonella typhimurium are most common, antimicrobial therapy can be helpful.

Whatever treatment you and your veterinarian select, always try to disinfect any equipment used to administer treatment between animals. The most common piece of equipment that spreads salmonella is esophageal feeders, says House. Producers use the same feeder to give fluids to a sick calf and then to give colostrum to a newborn.

The biggest thing is to keep the animals eating. Remember, when dry matter intake drops for any reason, the level of VFAs in the rumen also drops. And high levels of VFAs are toxic to salmonella.

You can stop salmonella. Once you understand the culprit and make the appropriate management changes, you can limit the occurrence of salmonella, says Meadows. And, with diligent management, you can prevent any future death loss.

A formidable foe

Salmonella occurs readily in the environment and is quite hardy.

Keep these facts in mind as you develop protocols to help minimize its occurrence:

1. Salmonella dublin can manifest as a pneumonia outbreak in calves.

2. Researchers have taken dry bedding, wet it, and waited 24 hours and salmonella - when present in the environment - will start to multiply.

3. Commodity feeds and forages can harbor salmonella. In a herd under stress, these contaminated feeds can lead to a whole herd outbreak.

4. When you have one pen of salmonella cows and you re-circulate wastewater to flush pens you can spread salmonella throughout the dairy.

5. Salmonella can survive 150 days or more in a lagoon during warm weather. Proper aeration of the lagoon will help limit its survival time.

6. If you spread lagoon water - that has salmonella in it from a recent outbreak - you can
contaminate waterways and your forages.

Human concerns

Salmonella is a zoonotic pathogen, which means it can attack animals and humans - anything with an intestinal tract. The biggest risk is to children and older adults, or anyone with a compromised immune system.

To protect your employees and their families, use these rules:

1. Have employees wash up (preferably shower) and change clothes before going home. Or, if they go home to do so, make sure that it is the first thing they do before saying "hello" to their families and pets.

2. Do not let children visit the animals, especially do not let children allow calves to suckle on their fingers.

3. Do not allow anyone to drink milk from the bulk tank. Pasteurization kills salmonella.

4. Have employees wash their hands with soap and water prior to consuming food or fluids.